GRINDING WHEEL and ABRASIVES BASICS
General Abrasives - Construction and Identification
Grinding wheel specification
Grit type and color
Diamond and CBN Wheels
Diamond and CBN basics
Diamond or CBN wheel
only on carbides and CBN only on steels?
Contrary to what you may
think, the long codes associated with grinding wheels actually can be
interpreted and generally have a clear meaning. Most all
manufacturers will list the grit type, grit size, wheel hardness,
structure and the bond in every grinding wheel produced.
It is important to note that there is NO STANDARD among grinding
wheel manufacturers. Each will use their own unique identifying
method of marking; However, there are some common rules - at least
here in the USA. A typical grinding wheel specification might be
'A60-I10-VS'. 'A' is the grit type (in this case aluminum
oxide), '60' is the grit size, 'I' is the relative hardness, '10' is
the structure, and 'VS' is the type bond (VS for this company means
vitrified bond. There are
variations too. For example, one might see this '97C80 +F/-G
-B11-DC'. In this case, 97C is the grain/grit type (here 'C'
probably is silicon carbide), 80 is the grit size, +F/-G indicates a
zoned or graded wheel of an in-between hardness. -B11 is the
bond (B11 is probably a resin bond). The DC is some process done
to the wheel such as slots or grooves or holes or induced porosity.
Other suffixes are added by each individual manufacturer for special
conditions. Only by looking at the manufacturing record or
process sheet will anyone know for certain what exactly made up that
particular grinding wheel - The specification alone will not tell the
As noted above, generally one cannot take a grinding wheel from one
manufacturer that is marked similarly and substitute for another
manufacturer's grinding wheel of equal marking. In the first
place, it is highly likely they will not be marked similarly and
secondly, variations in factory production methods typically make
grinding wheels of different construction. Unless one is not
very picky about their grinding wheel or not doing exacting work and
is willing to accept some grief, we would not recommend anyone try to
make substitutions without some guidance from an engineer familiar
with the process and the manufacturers. This is where we come
in: We work with the factories to get you the proper grinding wheel.
It is also important to note that the end user should expect some
TRIAL & ERROR when converting from one brand of wheel to another.
Sometimes a manufacturer may need two or even three tries to finally
hit on the exact hardness, grit, bond, etc.. Patience and time
are key to any successful conversion and testing.
Grit type and color
Grit type is generally either aluminum oxide
(white, pink, ruby red, brown, grey, etc.) silicon carbide (black or
green), ceramic (blue and pink) or any combination of these.
Aluminum oxide is by far the most popular. It is available in
the following colors: White, pink, red, ruby red, brown, and grey.
Each color has it's own grinding characteristics. Grey and brown
grit are the workhorse grits used in bench grinding and production
grinding. Tough and inexpensive they are the most 'general
purpose' grit found. Can be used on low to high carbon steels.
The pink and white grits are typically used on your harder steels
which need a cool, friable cutting action to avoid burns. The
ruby red grit is a special tough grit also used on tool steels.
These grits are a little bit more expensive than the grey/brown.
Ruby red is very expensive. Silicon
Carbide grits are commonly either black or green. Black silicon
carbide is used to grind non-ferrous metals such as aluminum and brass
and also on plastics, rubber, and stone products such as marble and
granite. Black silicon carbide is a very sharp grit. Green
silicon carbide is an even sharper grit than black and is used
primarily for carbides, titanium and plasma sprayed materials.
One interesting characteristic of silicon carbides is the effect they
have on steels. Due to the sharpness of these grits, one would
think that they would be too aggressive and not provide a good finish.
In fact, on steels, silicon carbide is used as a sort of
polishing/finishing grit. It is used in tumbling processes as a
surface finishing product. Also, manufacturers will often blend
a small percentage of silicon carbide in with aluminum oxide grit in
grinding wheels and honing stones to achieve a better workpiece
surface finish on steels. The grit will actually dull and
provide a rubbing action on steels which produces a better surface
A newer grit that is
available is ceramic (also referred to as SolGel® or SG®). Ceramic
grit has the characteristic of not dulling -- It will break down or
fracture into sharp corners rather than dull and pull out of the bond.
This makes the wheel typically last longer and it will also provide
excellent aggressive stock removal without heat build up. This
grit is only made by a couple of producers and is very expensive,
typically two or three times as expensive as aluminum oxide. You
will normally not see a 100% ceramic grit wheel. The grit is
typically mixed with aluminum oxide in various percentages from 10% up
to 50%. Ceramic is used in tool steels and lower carbon steels
equally well. These grinding wheels typically require a good bit
of custom engineering for your specific application and process to
achieve profitable results.
Grit types are sometimes
mixed in combination for achieving certain cutting characteristics.
Grits are also called friable (white) or semi-friable (pink, brown and
grey, red, etc.). Friable grit breaks down more easily and is
useful for cutting harder materials.
Grit size typically runs from coarse (16 -24 grit),
medium (36 - 60 grit) and fine (80-120 grit). Superfine grits
run from 150 and higher. Grinding wheels usually will be between
24 and 100 grit. Honing stones and jointing stones and other
polishing abrasives will be 150 grit and higher. Use a coarse
grit for fast, aggressive stock removal and finer grits for less stock
removal but better surface finish.
Hardness is rated from A-Z
with 'A' being the weakest bond and 'Z' being the strongest. A
weak bond is preferred for grinding harder materials while a
stronger bond is desired for softer materials. A typical weak
bond for steel would be in the 'F, G or H' range. A medium
hardness would be in the 'I, J or K' range. And stronger bonds in the
'L, M, or O' range. Hardness is dependant on the grit type, the
material being ground, the amount of stock removed, and a number of
Hardness grades are typically
linear: If you increase the hardness by one letter grade (An H to and
I for instance) it could give you double the wheel life. Many
people mistakenly believe that such a move (from an H to an I) would
only be marginal -- Don't be misled here: A move of just one or two
hardness grades could have a dramatic effect on your process!
It is important to note that
it is almost impossible to match one grinding wheel manufacturer's
wheel hardness to another manufacturer: Differences in factory
kilns, measuring instruments and the lack of a standardized hardness
system do not allow for direct cross-overs. One company's 'G'
hardness would be a 'F' with another and even a 'H' with another.
We get calls all the time on this: We simply cannot guarantee
one wheel to be the same as another. Even when our manufacturers
switch their production to a different factory in another state or
country we will see some variance. This can sometimes be
or grain spacing
Structure is basically the
spacing between abrasive grains. An open structure would be 12
or higher while a closer structure would be 6 or so. Here again,
the structure depends on a variety of factors not the least of which
is how difficult the material is to grind. One would think that
a closer spacing would make a tougher wheel but this is only true to a
point: With less bond holding the individual abrasive grains, the
softer the wheel would be. Also, the same holds true for a very
open structure: If the grains are wide spaced you have fewer grains to
grind with but a greater amount of bond holding each grain -- This
could make the wheel tougher. Grinding wheel engineers will
typically adjust the BOND STRENGTH depending on the application.
There are various bond types
but the most common are vitrified and resin. Vitrified is
basically a vitreous glass much like pottery or glassware fired in a
kiln. Resin wheels are plastic resins mixed and cured at lower
temperatures. Vitrified wheels are commonly used for bench,
surface and tool room applications such as surface grinding while
resin wheels are commonly seen in cutoff wheels, centerless wheels and
superabrasive wheels (diamond & CBN). Newer bonds are Plastic
bonded wheels based on high technology from companies such as
Diamond and CBN basics
Diamond and CBN wheels come in several bond types:
Resin (most common), vitrified, metal and electro-plated. Resin
is used in most tool room and production applications. Vitrified
and metal bonds are newer bond types with specific applications (We
won't go into a lot of detail with these as they are somewhat rare and
more expensive and almost always are custom made special order items).
Electro-plated wheels are very common and are typically found in
cutoff wheels and low demanding abrasive grinding such as for
Resin wheels are made much like a traditional grinding wheel with a
thick bond/grit layer usually between 1/16" and 1/4".
Electroplated wheels are a much thinner thickness. In both
cases, the bond layer is applied to a hub which is either aluminum or
steel made to the specific profile required.
Like traditional grinding wheels, Diamond and CBN
wheels are used in a variety of processes and with a variety of
materials. Typically, diamond wheels are used strictly on
carbides and CBN is used on steels. Some manufacturers produce a
'hybrid' wheel which is a special grit that will grind both steels and
carbides (Typically used on parts that require grinding of carbide and
steel at the same time). Plated diamond wheels are used on
non-ferrous materials such as plastics, rubbers, nylons, fiberglass,
Identifying your diamond or CBN wheel
Diamond and CBN wheels are classified by their
shape, grit size, concentration and the bond. A typical diamond
wheel specification might be D1A1-150R100-B4 where D1A1 is the wheel
shape, 150 is the grit size, 100 is the concentration and B4 is this
particular manufacturer's bond (B4 is most likely a resin bond).
Grit sizes of 120 to 180 are typical for tool room applications.
Finer grits of 220 or above are generally special order and for
extremely fine finish work.
The concentration is, in layman's terms, simply the amount of grit in
the mix. Concentrations of 75 or higher are preferred but it
also depends on the specific application. Some jobs may do
better with less concentration. Generally, the higher the
concentration the longer the wheel will last and the more expensive it
will cost up front.
Bonds are weak or strong depending on the application but usually
there is one main bond for 90% of the wheels made. Exotic bonds
like copper and polyamide are very expensive and are utilized in
demanding, precise operations where close attention is paid to both
wheel life and wheel cost. Typically, a manufacturer will need
to know if a diamond wheel will be run in coolant or dry -- This
determines the bond. CBN wheels should always be run in coolant.
You will also see in the specification a callout for the bond layer
thickness, for example: "X=1/8". This is very important in the
life of the wheel and it's initial cost. A bond layer of 1/8"
thick will be half the thickness of 1/4" thick and thus half the life.
Some manufacturers will supply wheels with as little as 1/16" or as
much as 1/2". The most common are 1/8" and 1/4". The price
can vary dramatically and this is an important factor to consider when
comparing wheels from one company to another.
Diamond wheel on steels
and CBN on carbides?
We get asked quite frequently
if a diamond wheel can be used on steels and CBN on carbides. We
do not recommend this as the wheel life will be greatly reduced and in
some cases, the wheels may not even cut at all. A diamond wheel is
specifically used for carbides, plastics and other synthetic
materials. It will not grind steel well at all. CBN wheels
should only be used on steels. There is a hybrid grit available
that will grind both; However, it is a compromise in wheel life and
grind-ability. But in cases where you must grind both materials
at the same time, it can be a real time saver.
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